Line up allowance

[73qanda]

Hi there,
Our Performance Manual tells us that the line up allowance for our 737-800 aircraft is 27m (ASDA) and 11m (TORA) . For an intersection departure, where does that 11m start from? Is it abeam the centreline of the taxiway ( where it enters the runway) even if the taxiway you are entering on is a high speed exit?
If someone could point me towards an ICAO doc that explains I would be grateful.
Cheers

[Sir George Cayley]

Don't know about ICAO but the UK CAA equivalent to Annex 14 has some useful drawings.

Google CAP168 Fig 3.14

[TheiC]

Sir George has it; this was clarified recently in the UK's freely-published CAP.

Practically-speaking, following the taxiway centreline and then a sharp ninety-degree turn onto the runway centreline will give you the appropriate distance ahead. The crucial thing is not to follow the lead-off line as though it's a lead-on line. An exception would be doing so at a trot or canter, with the intention of a rolling takeoff, when a gentler turn at higher speed leaves you going faster at a particular point than you would have been had you turned on sharply at low speed. Doing so whilst spooling up may be VERY bad for some engines.

It's a complete mystery to me why ICAO doesn't make its safety standards available to people to read and learn from.

[73qanda]

Thanks a lot . I found the nice drawing in the cap which was a bit different to what I expected in that it used the downwind side of the taxiway as the reference for extending through to the runway centreline.
I am in NZ but imagine we have adopted ICAO for most things aviation.
Thanks again.

[AerocatS2A]

Why would you use the upwind side? That robs you of tens of meters of TORA.

[73qanda]

Good question Aerocat. Who thought it would be a good idea to use the upwind side? Was the post deleted?

[Piltdown Man]

Unless you are performance limited, why not plan for an intersection departure and use the next longest one (or more) or reduce your TORA/TODA by 100m or so? Then you don't have to scrub your tyres and strain the gear graunching the aircraft around on the runway to squeeze every metre available. It also allows for a smooth, gentle line up and rolling takeoff.

[73qanda]

Unless you are performance limited, why not plan for an intersection departure and use the next longest one

I agree that that is a good idea in some circumstances, it's something I do if there will be no time penalty.

or reduce your TORA/TODA by 100m or so?

That isn't an option with the OPT we use.
Thanks for the input.

[AerocatS2A]

Unless you are performance limited, why not plan for an intersection departure and use the next longest one (or more) or reduce your TORA/TODA by 100m or so? Then you don't have to scrub your tyres and strain the gear graunching the aircraft around on the runway to squeeze every metre available. It also allows for a smooth, gentle line up and rolling takeoff.

If you fly something with lack lustre performance you might not be able to get full flex from the next intersection down which makes management unhappy. So although you do have some performance margin you can't quantify it in terms of a reduction in TORA and have to treat it as though you have no performance margin at all.